Microtechnology | EPFL Graph Search

Microtechnology deals with technology whose features have dimensions of the order of one micrometre (one millionth of a metre, or 10−6 metre, or 1μm). It focuses on physical and chemical processes as well as the production or manipulation of structures with one-micrometre magnitude. Development Around 1970, scientists learned that by arraying large numbers of microscopic transistors on a single chip, microelectronic circuits could be built that dramatically improved performance, functionality, and reliability, all while reducing cost and increasing volume. This development led to the Information Revolution. More recently, scientists have learned that not only electrical devices, but also mechanical devices, may be miniaturized and batch-fabricated, promising the same benefits to the mechanical world as integrated circuit technology has given to the electrical world. While electronics now provide the ‘brains’ for today's advanced systems and products, micro-mechanical devic

Mechanical principles of engineering fibrous tissues with programmable shape

Erik Mailand

The form and structure of biological tissues define their function. The emergence of tissue morphology during development is one of the wonders of nature. Cells mechanically probe and manipulate their surroundings while constructing structures from the extracellular matrix that they produce. Self-assembly of tissues is essentially a mechanical process, touching various engineering disciplines including solid and fluid mechanics as well as thermodynamics. Recent advancements in materials science, molecular biology, and microtechnology enabled the engineering of living tissues in vitro as a means to discover the physical principles of morphogenesis. The quest is far from being completed, particularly for the cases where cells are interacting through a fibrous matrix. There is no algorithm or protocol that can prescribe long-lasting shapes to these constructs with arbitrary complexity. Considering the potential impact of this endeavor in regenerative medicine and drug screening, novel perspectives are urgently needed. The objective of this thesis is to provide an experimental and computational framework that would together enable the researcher to perform system identification and sculpturing on small scale biological samples. System identification involves dissecting the contributions of forces and motion on the evolution of the tissue shape. Sculpturing living matter means guiding the morphogenesis process through pre-programmed mechanical perturbations. Computational modeling of tissue mechanics aid both the interrogation and engineering phases. As the biological sample, a very simple composition that is based on a cell-laden collagen gel was used. Two novel technologies are introduced: (1) a fully-motorized robotic micromanipulation system and (2) a spatiotemporally resolved optochemical stimulation protocol. The platforms are integrated with modern imaging systems for real-time recording and automation. The thesis starts with a detailed investigation of constrained fibrous microtissues where the emphasis was placed on the controlled perturbation of the mechanical state. Experiments revealed an opportunity and an important challenge. The study showed that surface stresses were as important as bulk stresses in the equilibrium configuration of the tissues. A physics-based computational model was developed that accurately captured tissue morphology by only considering bulk and surface contraction. The challenge is that tissues under the influence of these contractile stresses are inherently unstable and they are always inclined to deviate from the prescribed shape. Epithelial tissues undergo a fluid to solid transition. In the second part, this transition was harnessed to stabilize the tissue shape and enable reshaping upon mechanically induced fluidization. Unconstrained fibrous microtissues with an epithelial shell were successfully morphed into prescribed shapes and re-shaped under the guidance of precise mechanical manipulations. The final part of the thesis suggests various future directions that would capitalize on the presented results and advance the concept towards a robust and versatile tissue engineering solution.

EPFL2021

A new versatile hybrid MEMS technology for high sensitivity, fluid proof sensing applications.

Matthias Neuenschwander

The field of micro electromechanical systems (MEMS) evolved from the microelectronic industry and the technologies developed to fabricate integrated circuits. As a result, MEMS are commonly fabricated on silicon wafers. The development of MEMS has been driven by three main merits: miniaturisation, microelectronics integration, and parallel fabrication with high precision. Many operational properties scale well with smaller sizes. In addition, integrated electronic circuitry allows embedding MEMS with computing or networking capabilities, while parallel manufacturing enables the fabrication of many identical devices on a single wafer, reducing the unit cost. The main MEMS application is transducers which transform signals from one form of energy to another, and can be used for perception (sensors) or to produce actions (actuators). Silicon and other microelectronic materials like metals have enabled very high-performance MEMS transducers because these materials can be used for a range of very effective actuating and sensing principles.More recently, polymers have started to be used in MEMS because of their unique electrical, physical and chemical properties which include biocompatibility, viscoelasticity and mechanical shock tolerance. They are also much softer than silicon or metals, and they can be processed using many techniques that allow unique low-cost, batch-style fabrication and packaging. However, polymers have relatively low glass-transition and melting temperatures. As a result, the advantages of polymers cannot easily be combined with high-performance actuating and sensing elements as these are based on silicon technology and require high-temperature fabrication steps. Here, a hybrid-MEMS fabrication process is used to address this issue. The developed devices are based on a trilayer structure, where a thick polymer core is sandwiched between two hard thin films, while electronic layers are embedded within in a fluid-compatible way.The objective of this thesis is to turn hybrid-MEMS into a benchmark MEMS technology. This involves many different aspects. First, sensing and actuation elements are integrated into trilayer devices, and their performance is analysed. Then, some more unique possibilities offered by hybrid-MEMS are exploited. A way to fabricate electronics on multiple layers is developed, which allows different electronic features to be integrated in parallel. In addition, three-dimensional bulk features fabricated at several levels are demonstrated. This is possible because the hybrid-MEMS process is based on the bonding of multiple wafers.All these new fabrication features are demonstrated in atomic force microscopy (AFM) applications. Self-actuated trilayer AFM cantilevers with sharp silicon tips are used to boost imaging speeds in the off-resonance tapping (ORT) mode, thanks to an order of magnitude faster surface probing rates. Furthermore, fully integrated ORT imaging is demonstrated with self-actuated piezoresistive cantilevers. Next, trilayer cantilevers with shielded conductive tips are introduced for electrical AFM modes. Finally, ongoing research projects are touched upon, including approaches to fabricate hybrid-MEMS with single crystal silicon piezoresistors for improved sensitivity, and an analysis of reproducibility of fabricated trilayer cantilevers.

EPFL2022

Microfluidic devices for the study of cell-cell, cell-particle and particle-particle interactions

Margaux Catherine Marie Duchamp

Microfluidics and microtechnologies are of great interest for biological applications. This interest is linked to the fact that microtechnologies enable the study of single cells at the cellular and sub-cellular level. One of many applications of such single cell assays is cell-cell interaction probing. Current cell-cell interaction tools used by biologists rely on manual cell manipulation. But in the last decade new microfluidic technologies have arisen to tackle this biological challenge. Despite this growing need, the developped microfluidic devices still force biologists to compromise between the throughput of the assay (number of cell pairs interrogated) and the control over the interaction parameters (contact force and contact time). This thesis proposes an engineering point of view of microfluidic tools for single cell and in particular cell-cell interaction studies. The developed microfluidic devices enable an advancement of the microfluidic technologies to leverage new tools for cell-cell interaction interrogation in a controlled manner and at a high throughput. In this work we report the development of a novel microfluidic device based on a “roll-over” mechanism. This new chip design enables the multiplexing of cell-cell interactions. This multiplexing is achieved by forcing into contact all cells from a sample of a first cell population with all cells from a sample of a second cell population. Using such a device, we characterized the interaction of cells expressing olfactory receptors. This chip enables the maximization of cell-cell interaction interrogation and thus is ideally suited for rare and nonredundant cell populations. A droplet microfluidic chip for controlled and reliable cell co-encapsulation was designed and implemented. Common droplet microfluidic devices rely either on random cell co-encapsulation in droplets, thus leading to high cell loss, or use multiple microfluidic devices sequentially to perform droplet manipulation steps and achieve cell co-encapsulation. Both cases lead to cell sample loss, first from the random cell co-encapsulation process and second from the possible droplet loss between different microfluidic devices. Therefore, the implementation of a single fully integrated device enabling controlled cell co-encapsulation in droplets is of high interest for the study of precious, large cell libraries interactions for example in the case of cancer immunotherapy. In this thesis we also developed new concepts, using already existing microfluidic designs. By reusing the microfabrication technologies and microfluidic principles of the previously designed devices we could develop a novel microfluidic chip for another biological application. The third device studied in this thesis enables to look further into cell membrane receptors by isolating plasma membrane fragments. This tool enables an in-depth study of receptors involved in cell-cell interactions. It can also be used for any other cell membrane receptor study as for example G protein coupled receptor screening for therapeutic drug discovery. The tools developed in this thesis set the grounds for the development of new generations of cell-cell interaction microfluidic devices, enabling high throughput and control over the cell-cell interaction parameters. The technological advancements presented in this work were validated for various biological applications.

EPFL2020